The need to add new customer service branch pipes to existing main gas or water utility pipelines has long been recognized. The safest method is to isolate the section of main pipeline, depressurize, purge, cut a hole, clean out, and permanently attach a tee adapter to which the branch pipe can be attached while the pipeline is depressurized. However, to reduce service interruptions to existing customers connected to the main pipeline, hot tapping tools have been developed for metallic pipelines that can drill or cut into the main pipeline while still in service under gas or water pressure. Prior art for hot-tapping a main plastic pipeline involves attaching a pipe saddle fitting to the main pipeline and then attaching an appropriate tubular adapter having a flange, or some type of mechanical joint outlet connector, to the pipe saddle fitting. Finally, a short length of branch pipe is connected to the tubular adapter, and a hole is drilled in the main pipeline for fluid communication with the branch pipe. A tapping tool, which includes a compression seal butted against the open end of the branch pipe, a drill mounted on a shaft extending through the compression seal and the pipe saddle, and means to advance/retract the drill bit from outside the fitting, is then used to drill the hole in the main pipeline. After the hole is drilled, the drill bit is retracted toward the compression seal within the now pressurized length of branch pipe. If a full flow valve is not included in the branch pipe, a squeeze off tool is used to seal the branch pipe near the pipe adaptor, before removal of the tapping tool. After attaching the remainder of the branch pipe to the tapped section, the full flow valve is opened, or the squeezed section of the branch pipe is rerounded. Use of hot tapping tools has become so common, especially in water distribution, that the manufacturers of the tools have developed dimensional standards for hot tap tools offered for sale.
Several problems, however, are inherent in the prior art techniques for using the standard hot-tap tool on plastic pipelines. The use of the hot-tap tool requires extensive evacuation/back filling for buried pipelines, such that restricted access may prevent installation of the hot tap tool in some locations.
Another problem is that commercially available plastic pipe saddle fittings and plastic tubular adapters having flange or mechanical joint outlet connections are of lengthy and bulky construction. Accordingly, when an available plastic tubular adapter is fused to an available plastic pipe saddle fitting, the passageway of the resulting assembly, through which the drill bit of the tapping tool must pass, is too long to allow use of many commonly sized tapping tools.
Other problems arise because commercially available plastic pipe saddle fittings lack sufficient mass, especially in the base section of the saddle, to overcome the weakening effects of a hole cut in the main pipeline. Once the hole in the main pipe has been cut and the coupon removed, the lack of sufficient mass in the base of the saddle fitting also results in inadequate contact surface for fusion to the main pipe. Accordingly, the lack of contact surface and/or reinforcing mass in the plastic saddle, result in failure of the fitting to provide a pressure rating equal to that of the main host pipe.
Accordingly, a need for a single compact plastic fitting exists. The single fitting desirably integrates the pipe saddle fitting and an appropriate outlet adapter in a single piece having suitable dimensions and strength, by which a tap for a service branch connection may be made into a plastic pipeline using hot tap tools of commercially available dimensions.
It is an object of this invention to provide a permanent saddle fitting of the type described above which is formed as a monolithic unit.
Another object is to provide a permanent pipe fitting for attaching a branch pipe that simplifies temporary use of a standard size hot-tap tool.
It is another object of this invention to provide a fully pressure rated branch outlet connection to a plastic pipe main.
Yet another object of this invention is to provide a fitting for a hottap tool where the fitting does not require temporary clamping of a saddle to the main pipeline.